Tetrafluoropropene represented by formula (1) CF3CX═CHX wherein Xs are different from each other and represent H or F is known as a useful compound, such as for refrigerants, solvents, and foaming agents. Of the tetrafluoropropene represented by formula (1), 2,3,3,3-tetrafluoropropene (HFO-1234yf) represented by formula CF3CF═CH2 and 1,3,3,3-tetrafluoropropene (HFO-1234ze) represented by formula CF3CH═CHF have shown promise as refrigerants with a low global warming potential.
As a method for producing tetrafluoropropene represented by formula (1), the following method, for example, is known: the method that allows monochlorotrifluoropropene represented by formula (2) CF3CY═CHY wherein Ys are different from each other and represent H or Cl (a starting material) to react with a fluorinating agent, such as anhydrous hydrogen fluoride, in the presence of a catalyst (see PTL 1).
Tetrafluoropropene represented by formula (1) is produced, for example, by a gas-phase continuous reaction of monochlorotrifluoropropene represented by formula (2) in the presence of a catalyst. However, this method is known to cause degradation of the catalyst when the reaction is maintained for a long time (see PTL 2).
The degradation of the catalyst is believed to be caused by decomposed matter or polymerized products adhering to the catalyst surface that result from decomposition or polymerization of monochlorotrifluoropropene used as a starting material, by-products generated in the reaction, and the like.
To reduce this degradation of the catalyst, for example, a method is reported in which the decomposed matter or polymerized products are removed by supplying an oxidizing agent, such as oxygen gas or chlorine gas, to a reactor (see PTL 1 and 3).
However, the use of oxygen gas for reducing the degradation of a catalyst requires the supply of a large amount of oxygen relative to the amount of the supplied starting material, and the inhibitory effect on catalyst degradation is also not considered to be satisfactory. Additionally, a lower selectivity of the target product may result in the use of chlorine gas for reducing the degradation of a catalyst, because chlorine gas, due to its high reactivity, may react with the starting material compound and the like.
Because of the problems described above, there is demand for a method for producing tetrafluoropropene represented by formula (1) by reacting monochlorotrifluoropropene represented by formula (2) as a starting material with anhydrous hydrogen fluoride in the presence of a catalyst, the method being capable of maintaining the conversion of the starting material and the selectivity of the target product within an excellent range, while reducing degradation of the catalyst to maintain the reaction for a long time.